Oil is removed from underground reservoirs after the drilling of a wellbore. In the past, wellbores were approximately vertical. Perforations were made in the casing to permit oil to flow into the wellbore from the reservoir. The inlet for the pump was lowered on tubing to the region of the wellbore below where the oil entered the wellbore and the liquids were pumped to the surface.
A more recently developed technique for oil extraction involves the drilling of a wellbore into an oil reservoir at an angle to the vertical. In some cases the wellbore is approximately horizontal. Oil in reservoirs contain gas and are accompanied by free gas. When liquids are produced along horizontal or inclined wellbores, the gas separates and is located at the top of the wellbore. Liquid oil is present along the lower portion of the wellbore.
Conventional pump inlets, when used in inclined or horizontal wellbores, usually entrain both liquid oil and gas. This results in inefficiencies in pumping because the gas occupies space in the pump. The entrainment of too much gas can cause "gas locking" which may result in temporary stoppage of flow through the pump.
Prior art systems have been devised to address the aforenoted problems. For example, larger pumps were used to try to overcome the inefficiencies of pumping. Another proposed solution was the design of devices to separate the gas from the liquid within the pump inlet as shown in U.S. Pat. No. 5,113,937 issued on May 19, 1992, which uses a device attached to the free end of the pipe stem attached to the pump inlet. The device uses a check valve system and pressure differentials to draw liquid from different parts of the device but would not readily function in a horizontal wellbore to efficiently pump the liquid oil from the bottom portion of the wellbore.